I have used an Apple Time Capsule for a few years now to back up three Macs and it has been absolutely trouble free. Additionally I have had the occasion to do a complete restore of one machine when its hard drive cratered and I have often retrieved individual data files on any one of the three machines. Building the "time" universe can sometimes take a bit long and that is exacerbated by the time lag on the network, but it just takes a little patience.
Many people like clones and I too have a clone of my system, but to be honest, it tends to get badly out of date and a clone is merely a snapshot in one instance of time whereas the Time Machine backup consists of hundreds or even thousands of instances in time. Far more flexible.
Having PCs on the network should have zero impact on the Time Capsule backups, but I would not attempt to back the PCs up to the Time Capsule. It needs to be pristine Apple.
